As known, the decay of building materials (marble, sandstone, bricks, etc.) and of decorative and artistic articles manufactured from these materials is determined by various phenomena both physical and chemical in nature which mainly occur in the presence of water. In order to effectively exert its function, a consolidating/protective agent must then primarily markedly reduce the extent and rate of penetration of water into the interior of the material to be protected. On the other hand one must prevent that the protective layer, while exerting said action, simultaneous induce collateral decay phenomena or however undesirable secondary effects. The essential characteristics of a good consolidating/protective agent can therefore by summarized as follows:
1. Ability to restore the cohesion between the particles of the surface layer of the decayed material and the underlying integral part. PA1 2. Exhibiting an adequate mechanical strength of the so consolidated surface layer. PA1 3. Retaining characteristics of elasticity within the consolidated surface layer in order to prevent the formation of a stiff surface layer having mechanical characteristics different from the substrate. PA1 4. Chemical inertia toward the material to be protected and consolidated. PA1 5. Low volatility. PA1 6. Stability toward the action of atmospheric agents, of light and of heat. PA1 7. Not altering the chromaticity of the material. PA1 8. Preserving for a long time its solubility characteristics in order to assure the reversibility of the treatment. PA1 9. Maintaining a sufficient permeability of the treated surface to air and water vapor, in order to prevent alteration phenomena underneath the impermeable film, due to condensed water within the interior of the same materials. PA1 (a) 55-98% by weight of an elastomeric copolymer of vinylidene fluoride comprising, in moles, 55-85% of vinylidene fluoride (VDF), 15-45% of hexafluoropropene (HFP) and 0-30% of tetrafluoroethylene (TFE); PA1 (b) 2-45% of a non-elastomeric polymer selected from a non-elastomeric VDF based (co)polymer, or polyvinylfluoride (PVF), or acrylic resins, for example polyalkylmethacrylates and copolymers of alkylmethacrylates with alkylacrylates, having T.sub.g &gt;50.degree. C.
It is known the use of perfluoropolyethers as protective agents for manufactured articles in stone and concrete, as described for example in U.S. Pat. Nos. 4,499,146 and 4,745,009. Said products, while solving the problem of protection, do not however exert a consolidating function due to their liquid nature. A consolidating action has been achieved by using polymers based on vinylidene fluoride, which effectively exert both a protective function and mainly a consolidating action. As described in U.S. Pat. No. 4,764,431, this result is obtained by applying on the material to be protected and consolidated a solution in volatile solvents of a polymer based on vinylidene fluoride, preferably copolymerized with hexafluoropropene.
The Applicant, in a copending application, Italian Application No. 21613 A/90, filed in the U.S.A. on the same day of the present application, and incorporated herein by reference, has found that the application of a composition, formed of (a) a fluoroelastomer based on vinylidene fluoride and (b) a non elastomeric (co)polymer based on polyvinylidene fluoride or a polyalkylmethacrylate, provides for superior performance in terms of both protection and consolidation compared to the performance achievable by using the fluoroelastomer alone in solution.